ESD damage suspected...but strange

[fredcapo]

This may be one for Ripleys Believe it or not...or not...

My friend had a new low-end mixer plugged into the aux-in of his cheapo Harbinger HA80 mixer-PA w speaker connected. A Shure type mike was plugged into one channel of the mixer. Carpet on basement floor. All was working. He touched the mike and drew a very serious ESD spark that actually stung. The audio went dead. On examination, that channel of the mixer was fried. Others still functional. However the Harbinger PA that was connected to the mixer via aux-in was dead. I have it on the bench now, and the -15 V rail is down to -1v, +15 rail OK the unit only hums, but smell burning after on a few minutes.

I can understand the mixer channel getting zapped, but ESD passing thru to the aux-in of the PA amp...?

I plan to pull the op amp connected to the aux-in and see if the neg rail comes back.

Any thoughts? Thanks.

[g1]

He was not connected to any other piece of gear (like a guitar) except the mic?

[The Dude]

Or, ground lift adapters/snipped ground plug/faulty house wiring? The body of the mic should have been at ground potential already unless the system wasn't properly grounded.

Also possible: The ESD didn't take out the second mixer, but the pop/transient created by the first mixer did.

Edit: They weren't doing something silly like running a speaker output of the first mixer (powered?) into a line level input?

[drewl]

Check the input opamps on the channels used on both mixers.

[fredcapo]

For the record..I just had time today to lift the vcc minus lead on the 4558 in the aux in/out circuit, and the rail came back...so it got fried. I have some tl072's which I believe will work in there.